**Keywords**: Protection, water source quality, measures and countermeasures, South-to-North Water Diversion Project (Middle Route)
**Abstract**: Starting from the current status of water source quality in the Middle Route, this paper analyzes the existing problems in water resources protection and management, explains the importance of water environment monitoring and protection in the water source area, and then proposes methods and countermeasures for combining basin and regional approaches, strengthening unified water resources management, and ensuring the water source quality of the Middle Route from a macro perspective.
**1. Geography and Natural Environment**
**1.1 Geographic Location**
The Danjiangkou Reservoir is the water source for the Middle Route of the South-to-North Water Diversion Project, located in Hubei and Henan provinces. Its administrative region belongs to six counties and cities in these two provinces, with a water area of 750 square kilometers. About 50% of the reservoir area is within Hubei Province. The reservoir's backwater length is 177 km along the Han River and 83 km along the Dan River.
**1.2 Natural Environment**
The Danjiangkou Reservoir is a comprehensive reservoir for flood control, power generation, irrigation, shipping, and aquaculture, formed by the Han River and the Dan River, also known as the Han Reservoir and the Dan Reservoir. The general trend of the reservoir slopes from the northwest to the east. It is located in the subtropics, with a mild climate, abundant rainfall, and an average annual precipitation of about 1,000 mm, with 70%-80% occurring between May and October. The average annual inflow volume is 39.5 billion cubic meters, and the normal storage capacity at the designed water level is 17.5 billion cubic meters, indicating relatively abundant water resources.
**2. Water Environment Status**
**2.1 Water Environment Quality**
(1) The main water sources of the Danjiangkou Reservoir are the Han River, the Dan River, and their major tributaries. The Han River contributes more than 75% of the total inflow. For over 30 years, the Han River has provided abundant high-quality water resources. According to the analysis of water quality monitoring data over the past 30 years, especially the monitoring data from the last decade, the water quality upstream of the Danjiangkou Reservoir (above the Danjiangkou Reservoir) meets Class II or better standards, except for some sections where individual parameters exceed the Class III standard for surface water environmental quality. The proportion of rivers meeting Class I-III standards reaches 90.3%, while the Dan River reaches 93.2%.
(2) Currently, the Danjiangkou Reservoir serves as the drinking water source for the city of Danjiangkou and provides partial industrial and agricultural irrigation water for Henan and Hubei provinces. Based on recent monitoring data, 86% of the monitoring sections meet Class I-II water quality standards, 10% meet Class III standards, and 4% meet Class IV standards. Overall, the water quality is good. The Danjiangkou Reservoir is the largest artificial lake in Asia, with a massive storage capacity and strong self-purification capabilities, making it an ideal water source for the Middle Route of the South-to-North Water Diversion Project.
**2.2 Water Environment Monitoring**
(1) The responsibility for water environment monitoring of the Danjiangkou Reservoir lies with the Hanjiang Water Environment Monitoring Center of the Yangtze River Commission. Since the construction of the Danjiangkou Reservoir began in 1958, the Yangtze River Commission has conducted water quality monitoring and analysis on various sections of the Han River upstream to study the impact of water conservancy projects on the water environment. After the reservoir began storing water in 1967, additional water quality monitoring and analysis were promptly added at sections such as the dam. To investigate water pollution, multiple pollution source surveys have been conducted in eight counties and cities within the reservoir basin, collecting a large amount of basic pollution source data. Additionally, three comprehensive sampling analyses have been conducted to understand changes in water quality and sediment conditions after the reservoir was filled. Monitoring and analysis have been carried out on the main streams of the Han River and Dan River, as well as eight heavily polluted tributaries. Currently, the Yangtze River Commission has set up eighteen water quality monitoring sections in the Danjiangkou Reservoir, analyzing over fifty items. Since the reservoir involves three provinces, inter-provincial monitoring tasks have also been initiated. Monthly water environment monitoring data is provided to the state for use in the Middle Route of the South-to-North Water Diversion Project and the "National Water Environment Status Report."
(2) In recent years, to meet the needs of the Middle Route of the South-to-North Water Diversion Project, especially for evaluating the current status of the water environment in the Danjiangkou Reservoir and for environmental protection design, extensive water environment monitoring has been conducted at Taocha, the starting point of the Middle Route canal. Large-scale water environment surveys and evaluations have been carried out around the reservoir and its tributaries, and biological monitoring has been implemented in the reservoir area to further clarify the current status of the water environment in the reservoir basin. Over the decades, the Hanjiang Water Environment Monitoring Center has conducted extensive water quality surveys, monitoring, and evaluations, accumulating detailed and reliable water environment data for analyzing the water quality status of the water source area of the Middle Route of the South-to-North Water Diversion Project, providing a reliable basis for water source protection and environmental impact assessment.
**2.3 Existing Problems**
(1) Increasing point-source pollution poses potential threats to the reservoir area.
According to long-term monitoring data, due to its abundant water volume, large storage capacity, and strong dilution and self-purification capabilities, the water quality of the Danjiangkou Reservoir has consistently remained at Class I-II standards. However, with the development of local industries, especially the increase in private and individually owned enterprises, some tributaries of the reservoir have experienced varying degrees of pollution, posing pollution risks to the reservoir area. For example, the Shending River, a tributary of the reservoir, originates upstream from Shiyan City, which developed due to the automobile industry. Shiyan is the largest industrial city in the upstream watershed of the Danjiangkou Reservoir, accounting for about 70% of the pollution load in the reservoir area. Although industrial wastewater pollution has improved somewhat in recent years, according to monitoring results, the main pollutants in the Shending River—ammonia nitrogen, COD, BOD, and fecal coliform bacteria—are still exceeding standards, indicating that domestic sewage pollution remains severe. Seventy percent of urban sewage in the city is discharged into the Han River via the Shending River, becoming one of the largest pollution sources for the Danjiangkou Reservoir. Although the proportion of inflow water is small, the pollution ratio is high, and there is a possibility of increasing pollution. Another example is the Laoguan River, which experiences lighter pollution during the wet season but significantly worse pollution during the dry season, reaching Class IV-V water quality standards.
Local polluting enterprises continue to discharge wastewater beyond allowable limits despite repeated prohibitions, closely related to local interests. Due to the mountainous terrain and inconvenient transportation upstream and around the Danjiangkou Reservoir, people's environmental awareness is weak, leading to frequent pollution accidents, such as the cyanide spill incidents in the Xun River and Tieshan River upstream of the Han River in 2000, causing serious consequences.
(2) Lack of unified and effective operational mechanisms for water resources management.
Currently, the South-to-North Water Diversion Project (Middle Route) has begun, but as the water source area, the Danjiangkou Reservoir faces fragmented water resource protection and governance. The reservoir and its upstream areas involve three provinces: Henan, Hubei, and Shaanxi. There is overlapping in water resource management and monitoring departments, as well as overlapping monitoring sections, resulting in unnecessary waste and even conflicts between provinces, regions, and systems. Without a unified water resource management agency to coordinate, there is a lack of emergency response capability when pollution incidents occur, failing to meet the needs of modern water resource protection and management work. There is no unified mechanism for water resource management prioritizing national interests.
(3) Unreasonable layout of water environment monitoring, failing to play its proper role.
The Danjiangkou Reservoir covers a vast area with a static reservoir area of 750 square kilometers and more than 20 major tributaries. Currently, some water areas lack monitoring, unable to meet the needs of water resource protection and management. At the same time, when conducting a comprehensive evaluation of water resources across the entire reservoir basin, the representativeness is insufficient, making accurate evaluations impossible. Some water areas have overlapping monitoring, with significant differences in monitoring methods and capabilities among different places and departments, making it difficult to conduct scientific and effective evaluations. This not only causes waste but also fails to effectively resolve disputes related to water resource management, so it does not truly fulfill its supervisory and management role in water resource protection.
**3. Measures and Countermeasures for Water Resource Protection**
**3.1 Strengthening Unified Water Resource Management Through Legislation**
Due to the large scope of the Danjiangkou Reservoir’s controlled basin, each place and department focuses on local interests, making it difficult to consider the overall water resource protection of the entire basin. Although in recent years, recognition of water resource protection in the South-to-North Water Diversion Project water source area has improved in various places, when it comes to local interests, there still exists a mindset that prioritizes economic benefits and efficiency over environmental protection, focusing on short-term gains at the expense of long-term benefits—a clear characteristic. As the water administrative authority responsible for water resource protection and governance, the basin organization faces significant constraints in exercising its responsibilities and authorities.
China's new Water Law has strengthened the unified management of water resources, clearly stipulating that the basin organization is the water administrative authority and reinforcing basin management. Since the state has already clarified the legal status, the basin organization must assume its responsibilities, strengthen the unified management and coordination of water resource protection departments in the basin, and incorporate management work into a more detailed, scientific, and unified management framework prioritizing national interests. Therefore, considering the characteristics of the Danjiangkou Reservoir, the urgent task now is to expedite the formulation of relevant regulations for protecting the water source area, such as the "Regulations on Water Resource Protection in the Water Source Area of the South-to-North Water Diversion Project," to constrain actions affecting the water environment through policy and administrative measures. Formulating regulations ensures legality, so the basin organization must adapt to the requirements of law-based administration, strengthen legal responsibilities, and ensure the flow of clean water northward.
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